Physics beyond the Standard Model with the DSA-2000

TL;DR

This paper assesses the discovery potential of the DSA-2000 for physics beyond the Standard Model across axions, dark photons, DM substructure, and neutrino masses. It develops an analytic model for radio emission from axion clouds around neutron stars and forecasts reach to the QCD axion band in the mass window $m_a$ between $2.9\mu\mathrm{eV}$ and $8.3\mu\mathrm{eV}$ within the instrument’s $0.7-2.0$ GHz band. It also evaluates dark photon signals from BH superradiance, DM substructure constraints via pulsar timing arrays, and neutrino-mass inferences from FRB dispersion measures, projecting substantial improvements over current limits. The results indicate that during its five-year run DSA-2000 could probe QCD axion parameter space, tighten compact DM constraints by an order of magnitude, and triple cosmological neutrino-mass constraints via FRB-based measurements, making it a versatile platform for BSM tests in the radio and late-time Universe.

Abstract

The upcoming Deep Synoptic Array 2000 (DSA-2000) will map the radio sky at $0.7-2$ GHz ($2.9 - 8.3 \, μ$eV) with unprecedented sensitivity. This will enable searches for dark matter and other physics beyond the Standard Model, of which we study four cases: axions, dark photons, dark matter subhalos and neutrino masses. We forecast DSA-2000's potential to detect axions through two mechanisms in neutron star magnetospheres: photon conversion of axion dark matter and radio emission from axion clouds, developing the first analytical treatment of the latter. We also forecast DSA-2000's sensitivity to discover kinetically mixed dark photons from black hole superradiance, constrain dark matter substructure and fifth forces through pulsar timing, and improve cosmological neutrino mass inference through fast radio burst dispersion measurements. Our analysis indicates that in its planned five year run the DSA-2000 could reach sensitivity to QCD axion parameters, improve current limits on compact dark matter by an order of magnitude, and enhance cosmological weak lensing neutrino mass constraints by a factor of three.

Figures (12)

• Figure 1: An axion converts into a photon with frequency $f = m_a/2\pi$ in the presence of a static magnetic field $B_0$.
• Figure 2: Schematic of the NS geometry. The NS rotational axis ($\mathbf{\hat{z}}$), magnetic axis ($\mathbf{\hat{m}}$), and the line-of-sight ($\mathbf{r}$) are denoted by a dashed line, a blue arrow, and a solid black line, respectively. The misalignment angle between the rotational and magnetic axes, and the angle of observation with respect to the rotational axis, are defined to be $\theta_m$ and $\theta$, respectively, as described in the main text.
• Figure 3: Expected radio spectral flux density from axion-photon conversions in NSs, assuming $m_a/(2\pi)=1$ GHz and $g_{a\gamma\gamma}=10^{-14}$ GeV$^{-1}$, for each pulsar in the Australia Telescope National Facility pulsar catalog Manchester:2004bp, magnetars in the McGill Magnetar Catalog Olausen:2013bpa, the Galactic Center magnetar SGR J1745-2900 with $P=3.76$ s Kennea:2013dfaMori:2013ydaShannon:2013hla, and four recently identified long-period magnetars, including PSR J0901-4046 with $P=75.89$ s Caleb:2022xyo, GLEAM-X J162759.5-523504.3 with $P=18.2$ min Hurley-Walker:2022, GPM J1839-10 with $P=22.0$ min Hurley-Walker:2023, and ASKAP J1935+2148, with $P=53.8$ min Caleb:2024nrq. Pulsars and magnetars in the catalogs are denoted by dots, while long-period magnetars are denoted by stars. The background contours in grey are derived assuming $M_{\mathrm{NS}}=1\,M_{\odot}$, $R_{\mathrm{NS}}=10$ km, $\theta=120^{\circ}$, $\theta_m=10^{\circ}$, $\rho_{\mathrm{DM}}=0.4$ GeV/cm$^3$, $d=1$ kpc, and $B_0$ satisfying Eq. \ref{['eqn:magnetic_field_P_Pdot_relation']}. The NSs that are not expected to produce any observable flux with these parameters are colored in black. Here we note that PSR J0901-4046 and GLEAM-X J162759.5-523504.3 are not within DSA-2000's field of view.
• Figure 4: Projected $5\sigma$ upper limits on $g_{a\gamma\gamma}$ are shown assuming 10 hours of observation time ($\Delta t_{\mathrm{obs}}=10$ hrs) on the Galactic Center magnetar SGR J1745-2900 Kennea:2013dfaMori:2013ydaShannon:2013hla (red dashed), two long-period magnetars: GPM J1839-10 with $P=22.0$ min Hurley-Walker:2023 (orange solid) and ASKAP J1935+2148 with $P=53.8$ min Caleb:2024nrq (green solid), and an ordinary pulsar J0250+5854 with $P=23.5$ s Tan:2018rhg (blue solid), observed with DSA 2000. The properties of each target are listed in Table \ref{['tab:axion_DM_targets']}. Here, we assume $M_{\mathrm{NS}}=1 M_{\odot}$, $R_{\mathrm{NS}}=10$ km, $\theta=120^{\circ}$, $\theta_m=10^{\circ}$, and $\mathrm{SEFD} = 2.5$ Jy. The DM density near the NS is estimated using an NFW profile with a scale radius of $r_s=8$ kpc, with the Galactic Center magnetar's distance from the Galactic Center taken to be $R_{\mathrm{GC}}=0.1$ pc. Existing constraints from ADMX Asztalos_2010ADMX:2018ghoADMX:2018ogsADMX:2019uokADMX:2021mioADMX:2021nhdADMX:2024xbv, RBF PhysRevLett.59.839Wuensch:1989sa, UF PhysRevD.42.1297Hagmann:1996qd, CAPP Lee:2020cfjJeong:2020cwzCAPP:2020utbLee:2022mncYoon:2022gzpKim:2022hmgYi:2022fmnYang:2023yryKim:2023vpoCAPP:2024dtx, CAST CAST:2007jpsCAST:2017uphCAST:2024eil, globular clusters Ayala:2014peaDolan:2022kul, pulsar polar cap noordhuis2023novel, solar neutrinos Vinyoles_2015, MWD Dessert:2021bkvDessert:2022yqqBenabou:2025jcv, and MeerKAT Battye:2023oac are shaded in grey (see Ref. AxionLimits). The QCD axion parameter space is shaded in yellow Saikawa:2024bta.
• Figure 5: Schematic of axion cloud formation and associated radio emission. Vacuum gaps (cyan cylinders) are formed at the footpoints of open field lines, defined as field lines that extend beyond the light cylinder (black, dashed). These gaps host large and time-varying ${\bf E} \cdot {\bf B}$. The right inset shows a snapshot of ${\bf E} \cdot {\bf B}$ within the gap region, and the left inset shows a schematic of microphysical processes related to pair production ("CR" stands for curvature radiation and "SR" for synchrotron radiation). A fraction of axions produced in the gap execute bound gravitational orbits around the NS (gold, dashed) and resonantly convert to radio photons when they encounter the resonant conversion surface (red). The characteristic time between encounters of the orbit with the resonant surface is represented as $\delta \tau_{\cross}$.